杭电2001

#include <iostream>
#include <iomanip>
#include <cmath>
using namespace std;
int main()
{
double x1,y1,x2,y2;
double result;
while (cin>>x1>>y1>>x2>>y2)
{
result = sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2));
cout << setprecision(2) << setiosflags(ios::fixed) << result << endl;
}
return 0;
}